Heretofore, numerous versions of safety closures have been designed for the purpose of preventing children and other unknowledgeable persons from gaining access to dangerous household chemicals, medicaments and drugs, such as are conventionally packaged in containers for consumer use. One type of safety closure that has attained substantial commercial acceptance is that referred as a "squeeze-and-turn" type of safety closure. One type of such safety closures is referred to a "single sidewalled" closure, such as that disclosed in U.S. Pat. Nos. 3,376,991; 3,941,268 and 3,984,021. Such single sidewalled closures offer only limited versatility with respect to the style and design of the container with which they can be utilized. In other words, by virtue of the single sidewalled construction, both the internal threaded portion of the closure and the interlocking members, of necessity, are integral components of the same sidewall. Thus, in order to provide adequate flexibility to deform or distend the sidewall sufficiently to disengage it from the neck portion of the container, the sidewall must extend substantially beyond the threaded portion, which is rigidly engaged with the container neck portion. Also, to provide sufficient space to accommodate such deformation, the sidewall is necessarily flared outwardly from the neck of the container. Thus, the style and design of the closure is quite restricted.
The foregoing shortcomings of single sidewall squeeze-and-turn safety closures are overcome with so-called "double wall" squeeze-and-turn safety closures, such as those disclosed in U.S. Pat. Nos. 4,117,945 and 4,138,028, the disclosures of which are incorporated herein by reference in their entirety.
The safety closures of the aforementioned '945 and '028 patents feature the advantage of having a double sidewall construction in which an inner skirt sidewall is threadably engageable with the threaded neck portion of the container, i.e., the container "finish", and in which an outer skirt sidewall is resiliently deformable independently of the inner sidewall and also is provided on its interior surface with interlocking members designed to interlockingly engage the dispensing end of the container when the safety closure is in a fully closed and sealed position on the threaded neck portion of the container. The resiliently deformable or distensible construction of the outer sidewall is such that manual compression of the outer sidewall, at diametrically opposed locations angularly offset approximately 90 degrees from the diametrically opposite interlocking members, coupled with concurrent retrogressive rotation of the closure on the neck threads, will permit disengagement of the interlocking members and permit unthreading and removal of the closure from the container. Such a double wall closure permits placement of the closure interlocking member or members on the resiliently distensible outer sidewall of the double sidewall closure, thereby affording substantial advantageous variations in the overall length, style and configuration of the closure. In addition, the double wall type closure accommodates implementation of a variety of ancillary sealing features, if desired, such as those disclosed in the aforementioned '945 and '028 patents.
Such double wall squeeze-and-turn safety closures, like the prior single wall closures, have hitherto been constructed with sufficient wall thickness to maintain the "stiffness" necessary to pass child protocol regulations, such as inhibiting the possibility of accidental opening when the upper parts of the closure were bitten. This in turn has required more material, resulting in greater cost and weight of the double wall closure relative to a comparable single wall closure, in order to limit the amount of ovalization that can be created in the closure outer wall by application of a given amount of squeeze force in the outer skirt wall squeeze areas straddling the angular location of the locking lugs.
Another problem presented by the double wall squeeze-and-turn type safety closure versus the single wall type is the need to design sufficient radial clearance space between inner and outer skirt walls to enable vertical travel of the outer wall due to the outer skirt wall swing point, when squeeze-flexed, being at the inside top of the inner wall. This travel room requires a large radial clearance between the closure outer wall and container finish to enable sufficient outer wall deformation to create the degree of ovalization required for the lug unlocking action. The resultant large "radial standoff" of the outer wall from the closure finish thus increases the overall closure outside diameter, and also can create an additional problem of enabling children to gain purchase under the closure with their teeth, as well as creating a problem in terms of overall container design aesthetics.